Kidney/urinary tract stone disease (urolithiasis) is a major health problem throughout the world. Most of the stones associated with urolithiasis are composed of calcium oxalate alone or calcium oxalate plus calcium phosphate.
Many disease states are associated with an excess quantity of oxalate in the body including: primary hyperoxaluria, secondary hyperoxaluria, autism, vulvodynia, oxalosis associated with end-stage renal disease, cardiac conductance disorders, Crohn's disease, inflammatory bowel disease, colitis, urolithiasis, oxalosis associated with end-stage renal disease, sarcoidosis, asthma, COPD, fibromyalgia, Zellweger syndrome, bariatric surgery and other enteric disease states.
Oxalate may be absorbed through the whole gastrointestinal tract including the stomach, and the small and large intestines. Therefore removal of dietary oxalate in these organs is effective in preventing oxalate absorption. Absorption of dietary oxalate contributes to 10-70% of urinary oxalate secretion. It is believed that excess of concentrations of calcium oxalate is responsible for stone formation. Thus, by reducing the oxalate concentration the risk of stone formation will be decreased.
There are very few, if any, treatment strategies known to significantly decrease the risk of stone formation. The main approaches have been to limit dietary oxalate absorption by orally administering oxalate degrading enzymes or bacteria, which come into contact with the content of the stomach and the intestines. The challenge in providing such treatment is the harsh acidic stomach environment, which may degrade the enzyme so that it becomes ineffective at low pH and in a high pepsin activity environment. The intestines are also challenging due to the presence of trypsin and chymotrypsin and due to a pH approaching neutral pH. Most of the known oxalate degrading enzymes have activity optimum at pH at an acidic pH. The challenge when oxalate degrading bacteria are used is to pass the gastric environment without losing the activity of the bacteria and to have the bacteria colonized in the intestines. An attempt has been to orally administer an enteric coated composition.
All germ-like oxalate oxidases reported in the literature are acid active and oxalate oxidase reported with activity at pH greater than 7 has not been confirmed as a single purified protein with gene sequence. WO 2011/066282 describes oxalate-degrading enzymes derived from fungi. Examples 5 of WO 2011/066282 has not isolated the enzyme and no information about the protein sequence is given. The present inventors have tried to purify some of this enzyme, but failed.
Makoto K. et al. in Journal of the Institute of Brewing, vol 115, 2009, 232-237 describes enzymes derived from barley and malt, but conclude that the enzyme seems to be a flavoprotein (see page 235, 1st column). The present inventors have repeated the experiment described in Makoto et al. using exactly the same barley seed, but failed to find any oxidase activity at pH 7.4.
However, there is still a need for treatment strategies, which effectively reduces the oxalate concentration in the body.